1. Field of the Invention
The present invention relates to power converter, and more particularly, relates to the control circuit of the flyback power converter with active clamp.
2. Description of the Related Art
Flyback power converters have been widely used to provide power supplies for electronic products, such as home appliances, computers, battery charger etc. An active-clamp circuit has developed for the flyback power converter, that increases the efficiency of the flyback power converter. Nevertheless, the traditional active-clamp circuit can only achieve high efficiency for the heavy load. The drawback of the traditional active-clamp circuit is the higher power loss at the light load because of the high circulated current. The objective of this invention is to improve the efficiency of the flyback power converter by recycling the leakage inductance's energy of the transformer in the light load, and achieving the soft switching for the heavy load. Therefore, the flyback power converter can be operated in higher switching frequency for reducing the size of the transformer. The related prior arts can be found in “Clamped Continuous Flyback Power Converter”, U.S. Pat. No. 5,570,278; “Offset Resonance Zero Voltage Switching Flyback Converter” U.S. Pat. No. 6,069,803; and “Active-clamp circuit for quasi-resonant flyback power converter”, U.S. patent application 20110305048.